**2. Therapy with small molecules**

Since SLE is an autoimmune disease affecting multiple tissues and organs, the outcome of the disease is mostly unpredictable [21, 22]. The optimum management of SLE is preventing further tissue or organ damage, preventing flares, improving the quality of patients' life, and ultimately extending the lifespan of SLE patients. However, currently available therapy is mainly focused on treating symptoms,

including flares. Antimalarials, glucocorticoids, and other immunosuppressive drugs are among the current treatments [23].

#### **2.1 Hydroxychloroquine**

Hydroxychloroquine (HCQ ) belongs to the group of antimalarials. Among the oldest drugs used in SLE, chloroquine, and HCQ were introduced between 1953 and 1955 and these drugs are four aminoquinolines that are widely used to manage SLE [22, 24]. Antimalarial drugs are well-absorbed orally, and the half-life of hydroxychloroquine is around 40 or 50 days [25]. Although the mechanisms of action of antimalarial drugs in attenuating inflammation and clinical signs of SLE remain unclear, recent studies suggest a possible action on the lysosomes of the immune cells. Specifically, antimalarials increase the lysosomal vesicle pH, suppressing the antigen presentation and synthesis of inflammatory mediators, such as prostaglandins, cytokines, and chemokines [26]. One of the most beneficial effects of increasing lysosomal pH in antigen-presenting cells by antimalarials is the selective suppression of presentation of autoantigens by decreasing the binding of autoantigenic peptides to class II MHC molecules without affecting the responses against foreign antigens [26].

Similarly, chloroquine and hydroxychloroquine also inhibit Toll-like receptor (TLR) signaling in immune cells leading to reduced immune activation [27]. In addition, chloroquine treatment inhibits the production of pro-inflammatory cytokines, including TNF, IL-6, IFN-γ, IL-1β, and IL-18, in a lysosome-independent manner [28, 29]. Hydroxychloroquine reduces the serum levels of the leukocyte activation markers, including soluble CD8 and soluble IL 2 receptors [30]. Studies suggest that antimalarial agents might work as prostaglandin antagonists and inhibit the enzyme phospholipase A2 by decreasing inflammation [22, 31]. Chloroquine and hydroxychloroquine reduce dermatological manifestations, significantly protecting against skin damage by reducing the production of pro-inflammatory cytokines exposure to ultraviolet light. Moreover, chloroquine treatment also reduces matrix metalloproteinase activity and helps maintain extracellular matrix homeostasis in patients with SLE [32, 33].

HCQ is an inexpensive, well-studied, well-tolerated, and most valuable immunomodulator drug for SLE treatment. Several studies have been published on the efficacy of antimalarials in patients with SLE. Generally, HCQ is prescribed to all SLE patients with minimal contraindications or side effects, especially in patients with lupus nephritis, and is used to treat constitutional, musculoskeletal, and mucocutaneous involvement. Studies indicate that antimalarials reduce mortality in SLE patients of diverse ethnic groups [34–38]. Administration of HCQ significantly reduces the severity of SLE disease activity, which includes a reduction in active clinical involvements, serum markers, activity scores, and disease flares [39]. Randomized controlled trials (RCT) have demonstrated the benefits of HCQ in SLE, including a reduction in flares [40–42], improvement in arthralgia [41], cytokine profiles [29, 43–45], and disease severity [36, 46–49]. HCQ decreases SLE disease activity, including flares during pregnancy [39, 50]. Despite the fact that HCQ is well tolerated, it has been linked to a variety of side effects, including cardiovascular, hematological, neurological, ocular, and skin concerns [39]. HCQ reduces the recurrence of congenital heart block in anti-SSA/Ro-pregnancies in SLE mothers and can be used as a secondary preventative of fetal cardiac disease [51]. Furthermore, a combination of HCQ and mepacrine has a synergistic effect in refractory *musculocutaneous* lupus [52].

#### **2.2 Glucocorticoids**

Glucocorticoids are well known for their rapid action, potent anti-inflammatory, and immunosuppressive effects. They are part of treatment regimens for many autoimmune rheumatic diseases, including SLE. Glucocorticoids exert their action via genomic and nongenomic pathways [53]. The genomic pathway of glucocorticoids is mediated by the cytoplasmic glucocorticoid receptor, which binds to the glucocorticoids in the cytoplasm. After binding, the GC-cGR complex translocates inside the nucleus and binds to the glucocorticoid response elements present in the promoter of several target genes. The GC-GC complex decreases the transcription of inflammatory cytokines via the process known as transrepression and increases the transcription of anti-inflammatory genes by transactivation [53, 54]. The nongenomic pathway is mediated via the membrane glucocorticoid receptor, inhibition of the enzyme phospholipase A2, and alterations in the cell membranes leading to decreased lymphocyte proliferation and function [55]. While genomic mechanisms require 30 minutes for activation after administration of glucocorticoids, nongenomic mechanisms work within minutes after administration. Generally, activation of the genomic and nongenomic pathways depends on the dose of glucocorticoids. While low doses of glucocorticoids induce genomic pathways, very high doses induce nongenomic pathways of action. Specifically, the nongenomic pathway is activated at doses of more than 100 mg/day of glucocorticoids and it is sensitive to glucocorticoids, such as methylprednisolone and dexamethasone, which have five times more potent nongenomic effects than genomic ones [56]. Interestingly, the use of glucocorticoids in lupus dramatically improved the survival of patients [56, 57]. Glucocorticoids are considered primary therapy in achieving rapid control of active lupus. Studies indicate that pulse intravenous methylprednisolone reduces moderate to severe disease activity [58]. Oral prednisone at a dose of less than 30mg/day initially and then tapering dose between 2.5 and 5mg/day over a few weeks successfully treated SLE [59–63]. Specifically, pulses of methylprednisolone combined with other immunosuppressive drugs and HCQ were helpful in achieving rapid and prolonged lupus disease control [58, 64], resulting in the reduction of cardiovascular and global damage [58]. Glucocorticoids are the best therapeutic strategy during pregnancy in the case of lupus flares as their potent anti-inflammatory effect is not associated with teratogenicity but may increase maternal morbidity [65]. Although glucocorticoids have significantly reduced acute mortality in severe SLE, the high-dose treatment regimen for long periods has markedly increased adverse events and systemic infections, causing long-term damage. Extensive observational studies support that GC-mediated toxicity is mainly dependent on the dose and the duration of exposure [66]. It appears that doses lower than 7.5mg/day (prednisone equivalent) may be relatively safe for long-term maintenance therapy for glucocorticoids [66–68]. In contrast, using a high dose of glucocorticoids has been associated with the development of osteonecrosis, infectious complications, and even death [69–73].

## **2.3 Azathioprine**

Azathioprine (AZA) has been one of the oldest immunosuppressants. It is used in treating conditions, such as chronic inflammatory diseases [74], organ grafts, malignancies, and rheumatologic diseases [75]. It is a heterocyclic carbon– nitrogen aromatic compound belonging to the purine family of analogs. It is the only purine analog used in treating SLE [76]. Though its mechanism of action in

*Recent Advances in SLE Treatment Including Biologic Therapies DOI: http://dx.doi.org/10.5772/intechopen.105558*

immunosuppression is controversial, AZA and its metabolite 6-mercaptopurine (6-MP) inhibit the enzymatic conversion of inosinic acid to xanthylic acid and of adenylosuccinate to adenylic acid and are known to interfere with DNA replication and de novo synthesis of nucleotides. This inhibits the replication of T-lymphocytes, as they are deprived of salvage pathways [77]. A previous study reported that AZA could induce T-cell apoptosis by inhibiting the costimulatory signaling mechanism that results in T-cell anergy, thus mitigating the effects of autoimmune cells [78]. Azathioprine is used in SLE for the management of multiple active nonrenal manifestations and renal complications, such as lupus nephritis, and is safe for use during pregnancy. AZA alone has shown encouraging results in the treatment of SLE when combined with steroids to reduce SLE mortality and morbidity [79]. Although AZA and 6-MP have been evidenced to cross the placenta [80], several studies show that when AZA is given at a lower dose, it can effectively treat SLE without affecting the fetus or creating congenital abnormalities [81].

#### **2.4 Mycophenolate**

Mycophenolate is an antiproliferative immunosuppressant drug. As an inhibitor of inosine monophosphate dehydrogenase (IMPDH) that is both uncompetitive and selective, mycophenolic acid (MPA) does not incorporate into the DNA while inhibiting the guanosine nucleotide synthesis de novo pathway. It is cytostatic on lymphocytes as mycophenolic acid inhibits the critical dependency of the de novo pathway of purine synthesis, through which T- and B-lymphocytes proliferate. It is typically administered orally in the form of tablets, whether coated, delayed-release, or as a suspension, and as lyophilized or powder for injection. Similar to AZA, MPA's mechanism of action interferes with the de novo synthesis pathway of nucleotides, with a cytostatic effect on lymphocytes. Mycophenolic acid has a mean half-life of 8–16 hours and an MPAG metabolite half-life of 13–17 hours, but its route of elimination is not understood. It was introduced as a new drug in patients with lupus nephritis and renal problems who were unresponsive to conventional immunosuppressants [82]. MPA is available as a prodrug mycophenolate mofetil (MMF) and mycophenolate sodium (Myfortic) that increases MPA bioavailability and lessens gastrointestinal side effects, respectively [83]. MPA treatment has been reported to lessen the SLE complications combined with other immunosuppressive drugs, such as corticosteroids and antimalarials, when the disease was inadequately controlled with the previous non-MPA treatment regimens. Mycophenolate mofetil is most frequently used for induction or maintenance therapy of lupus nephritis and is effective in treating nonrenal symptoms as well. Typical symptoms of adverse effects include leukopenia, neutropenia, abdominal pain, diarrhea, nausea, vomiting, and dyspepsia. Mycophenolate has a potential teratogenic effect. Pregnancy case studies show that mycophenolate consumption during pregnancy causes major adverse effects including early, spontaneous, and elective terminations and abortions, fetal malformations and congenital defects, and premature and low-birth-weight newborns, [84]. As a result, female SLE patients have been prescribed AZA instead of mycophenolate when they become pregnant [85].

#### **2.5 Cyclophosphamide**

Cyclophosphamide (CP) is an inactive prodrug that requires enzymatic activation, which occurs by the hepatic cytochrome P-450 [86]. Cytochrome P-450 hydroxylates the oxazaphosphorine ring of cyclophosphamide, thereby generating 4-hydroxycyclophosphamide, which coexists with its tautomer aldophosphamide. Upon decomposition, this aldophosphamide yields phosphoramide mustard, which acts as the alkylating effector, thereby exhibiting the cytotoxicity of CP. Interestingly, immunosuppression with cyclophosphamide has been identified as effective against life-threatening autoimmune disorders, such as SLE. SLE is characterized by B-cell hyperactivation and subsequent autoantibody production, often accompanied by T-cell abnormalities [87]. Under these conditions, cyclophosphamide has been beneficial as it effectively suppresses B-cell activity and antibody production [86]. Clinical studies in murine and human models showed that cyclophosphamide was more effective than prednisone in stabilizing renal function when given orally or intravenously. Standardization of medication revealed that long-term courses of cyclophosphamide alone or in combination with high doses of corticosteroids had a lower probability of doubling serum creatinine and renal function preservation [86]. A 6-month treatment regimen with cyclophosphamide significantly improved renal function and complement activity. Over the last years, IV cyclophosphamide is one of the standards of care for induction of remission therapy that is used in severe lupus nephritis due to its ability to slow the progression to end-stage renal failure and it has been shown to be also effective for the treatment of severe nonrenal symptoms, such as vasculitis and myocarditis. While cyclophosphamide is beneficial, it should be noted that its administration is associated with significant adverse effects, including nausea and vomiting [88]. Cyclophosphamide, like other cytotoxic medicines, has teratogenic side effects. Among the most acute toxicities of CP are cytopenias, infections, gonadal failure, and malignancies [86]. Some infections, including herpes zoster, are more common than others in these patients; hence regular vaccinations are recommended. While the overall standardized incidence ratio of cancer is higher in SLE patients, administration of CP has been shown to increase the incidence of cancers, particularly those of the urinary tract, bone marrow, and skin, prompting the use of combination therapy to prevent these side effects [89]. A recent randomized clinical trial in Chinese SLE patients comparing cyclophosphamide and tacrolimus has shown that tacrolimus has a marginally higher rate of complete response and faster recovery of kidney function [90]. In contrast to this, another trial showed that combination therapy of cyclophosphamide with rituximab followed by belimumab not only lowered the maturation of transitional to naive B cells during B-cell reconstitution but also improved the negative selection of autoreactive B cells, thereby proving beneficial over the conventional cyclophosphamide and belimumab combination [91]. When cyclophosphamide is contraindicated due to a previous severe reaction or malignancy, or there is a concern for drug toxicity, mycophenolate mofetil or rituximab or belimumab is recognized as an alternative immunosuppressive agent to cyclophosphamide for the treatment of lupus nephritis.

#### **2.6 Voclosporin**

The use of calcineurin inhibitors (CNIs) voclosporin is an effective therapy against lupus nephritis, a common and serious consequence of SLE. CNIs bind to and inhibit calcineurin, a calcium-dependent phosphatase, preventing T-cell activation, and T-cell-mediated immune response leading to attenuation in the inflammatory process in lupus nephritis [92]. Voclosporin has a modified functional side chain and was found to have a fourfold increase in potency by inducing structural changes in calcineurin. The modification increased the effectiveness of this drug and improved

*Recent Advances in SLE Treatment Including Biologic Therapies DOI: http://dx.doi.org/10.5772/intechopen.105558*

the clearance of metabolites from the system. Thus, voclosporin was effective against lymphocyte proliferation, T-cell antigen presentation, and cytokine production [92]. According to the results of phase II clinical trial, females treated with voclosporin exhibited a 25% reduction in urine protein creatinine ratio after 8 weeks of treatment, as well as better complement activity after 24 weeks of treatment [93]. Interestingly, by the end of 24 and 48 weeks, the majority of patients had achieved remission, indicating that voclosporin was well tolerated in SLE patients. Another randomized double-blind placebo-controlled multicenter trial called AURA-LV, found that both low-dose and high-dose voclosporin administration promoted complete remission much more than the placebo group in a heterogeneous population [94–96]. Moreover, these patients had reduced anti-dsDNA antibody levels by 48 weeks, indicating the effectiveness of the medication. However, the study reported that patients receiving voclosporin experienced at least one adverse effect. Infection was the most common, under low-dose and high-dose administration, with a mortality of 5% [94]. Common adverse effects of the people who died in the low dose administration group include acute respiratory distress syndrome, infection, and thrombosis. Infection and pulmonary embolism were both common adverse outcomes in the highdose administration deaths, showing that this medicine could have safety concerns [94]. Furthermore, the AURORA1 clinical trial in lupus nephritis patients found that adding low-dose voclosporin to a regimen of MMF given with low-dose corticosteroids significantly improved the therapeutic effects, with stable kidney function and no increase in the incidence of adverse effects [97].

#### **2.7 Tacrolimus**

Tacrolimus is a calcineurin inhibitor studied for its effects against SLE [98]. Tacrolimus has been recognized for its immunosuppressive effects and has found extensive use as a post-transplant drug. Mechanistically, tacrolimus binds to FK-binding proteins in the cytoplasm, forming a complex associated with the calcium-dependent calcineurin/calmodulin complexes to inhibit calcium-dependent signal transduction lymphocytes and resultant cytokine production [98]. The initial report on tacrolimus' efficacy against SLE came from a patient study in which cyclophosphamide and cyclosporine treatment was shown to be ineffective. Tacrolimus treatment reduced creatinine levels and eliminated digital vasculitis and gangrene in these patients [99]. Furthermore, tacrolimus had a significant impact on treatmentresistant cutaneous lupus erythematosus [100]. Another study in mice with spontaneous lupus nephritis found that tacrolimus reduced proteinuria slowed nephropathy progression and increased the lifespan of the lupus mice. Moreover, tacrolimus reduced the elevation in anti-ds DNA antibodies seen in SLE patients [101, 102]. A previous patient study showed that patients administered with tacrolimus for a year had a significant decrease in the SLEDAI (SLE Disease Activity Index) compared to nontreated patients [103]. Moreover, patients exhibited decreased anti-dsDNA antibodies and increased C3 concentration, indicating improved complement activity. While these patients developed minor adverse effects, such as tremors and headaches upon tacrolimus administration, the effects subsided gradually, indicating the medication's effectiveness and safety [103]. In addition to its efficacy in SLE patients without renal involvement, tacrolimus was effective in pediatric SLE patients with lupus nephritis who had persistent disease activity despite conventional immunosuppressive therapy [104]. Subsequently, multiple studies showed the effectiveness of tacrolimus in SLE patients through its improvements in renal function and targeted

immunosuppression [98], thereby proving it as an effective therapeutic agent that functions against SLE through multiple mechanisms. In a meta-analysis of several randomized controlled trials, case-control studies, and cohort studies, it was found that tacrolimus in combination with glucocorticoids resulted in higher total remission rates, lower proteinuria levels, and a lower SLE activity index than cyclophosphamide, indicating that tacrolimus is a safe and effective therapy against SLE [105]. Another trial indicated that tacrolimus is as effective as and non-inferior to mycophenolate mofetil in reaching a complete renal response rate, demonstrating its value as a lupus nephritis induction therapy [106]. Combination therapy has demonstrated encouraging results in the treatment of patients with refractory lupus nephritis, with the potential to improve disease control and prevent lupus nephritis flares. Both mycophenolate mofetil and tacrolimus combination have synergistic efficacy and favorable adverse event profile; therefore, they can be utilized to treat refractory lupus nephritis.
